The present invention relates to a process for curing aminoplast resins, and more particularly to a process for curing urea-formaldehyde resins and urea-formaldehyde resins containing melamine.
Aminoplast resins, in particularly urea-formaldehyde resins are products which are well known in the wood industry. They are manufactured by various processes which involve condensing urea and formaldehyde under various conditions. For wood bonding, particularly in the case of the manufacture of agglomerated particle boards, a curing catalyst is added to these resins. The use of a mixture of this kind which is adhesive when heated and under pressure makes it possible to manufacture particle boards in the presence of wood chips. The curing catalysts employed in most cases are generally ammonium salts such as sulphate, phosphate and lactate, and in most cases, ammonium chloride.
The problems to be solved in the use of these catalysts for curing of aminonoplast resins are incompatible. If reactive catalysts are used, the production efficiency of the board manufacturing line is increased, but with the risk of curing the resin when cold. On the other hand, if it is desired not to run the risk of curing the resin when cold, a relatively unreactive catalyst will be chosen with the resin; the use of such results in a decrease in the efficiency of the production lime, since the resin will cure slowly when heated. It can be seen, therefore, that a compromise must be arrived at so as to made it possible to solve both the problem of the resin curing and that of the line production efficiency. To solve these problems it is necessary to have available catalyst which have a sufficient reactivity gap when heated and when cold.
There is therefore an appreciable need to develop a process for curing aminoplast resins making it possible simultaneously not to cure the resin prematurely, while retaining the possibility of curing the resin when the adhesive coated wood particles or wood plies are placed in a press and heated.